The present invention relates to thermostatic switches and more specifically to a thermostatic switch having an improved contact arm which reduces contact loading pressure and maximizes contact wiping action.
The general type of thermostatic switch contemplated herein has heretofore been known in the art. For example, a wide variety of thermostatic switches have been heretofore available which have generally comprised a pair of contacts, one of which is stationary and the other of which is mounted on a relatively simple, bendable contact arm which is operative for closing the switch by connecting the contacts. However, it has been found that the contact arm assemblies of the heretofore available switches of this type have suffered from several problems which can cause malfunctions and therefore reduce reliability.
One such problem which can cause malfunctioning of a thermostatic switch is cold welding of the contacts thereof due to high contact pressure. In this regard, many thermostatic switches of the prior art have utilized high contact pressures to maintain consistent contact over repeated contact cycles. It has been found that high contact pressures can cause the contacts of the switches to become welded together during periods of prolonged contact. Another problem related to high contact pressure is contact fretting or wear after repeated contact cycles. This is because the contacts of thermostatic switches are typically formed from soft precious metals, such as silver, and over repeated contact cycles, soft metal tends to fret or wear away reducing contact reliability and eventually leading to switch failure.
A further problem which can cause malfunctioning of thermostatic switches is microscopic contact fusion. Specifically, it has been found that when a switch is utilized for carrying high currents, material from the contacts thereof can often fuse together due to arcing.
A still further problem is the build up of layers of increased resistance on the surfaces of the contacts of a switch over repeated contact cycles which can also cause premature failure or discontinuities.